{an}等差数列,{bn}等比数列,公差公比均为d,且a1=b1,a3=3b3,a5=5b5,求{an}和{bn}?(d>0,d不等于1.)
问题描述:
{an}等差数列,{bn}等比数列,公差公比均为d,且a1=b1,a3=3b3,a5=5b5,求{an}和{bn}?
(d>0,d不等于1.)
答
设an=a1+(n-1)d bn=b1*q^(n-1)
a1=b1 a3=a1+2d=3a1 >a1=d,b1=d
a5=a1+4d=5d=5b1q^4>q^4=1
剩下的应该会了吧